1. Field of the Invention
The instant disclosure relates to a surface treated copper foil; in particular, to a composite dual blackened surface treated copper foil and method of manufacturing the same.
2. Description of Related Art
Large screen and high speed plasma display panel (PDP) has been widely used in a variety of display devices.
In general, the plasma display panel generates plasma from electrically charged ionized gases. The visible light is produced by exiting phosphors painted on the cells by ultraviolet (UV) photons. However, in the formation of visual image, in addition to UV photons, photons are also generated from near infrared range. The wavelength of near infrared light is close to the one used in the optic communication. As a result, near field interference may occur, for example, with microwave or super-low frequency electromagnetic waves.
The near infrared photon leakage or electromagnetic wave interference is reduced by the addition of a shielding layer made of copper foil in front of the display panel. The shielding layer is formed by the copper foil, which are etched into a mesh/reticular structure. However, the image contrast ratio is reduced because the copper foil shines and reflects external light. Furthermore, the copper foil reflects the internal light and leads to low light permeability, causing lower visibility.
The above mentioned problems are resolved by undergoing copper foil blackening treatment. However, only one side of the copper foil is treated in conventional surface treatment in conventional techniques. Thus, light reflection by the copper foil still exists on the untreated side. The untreated side is then processed in the subsequent fabrication process and the cost rises as well. In addition, because electronic components are minimized and arranged in high density, the wiring on printed circuit board is more compact. Laser drilling replaces traditional mechanical drilling to conduct more delicate pinhole formation on the printed circuit board. CO2 gas laser with a wavelength of 10 μm which causes nearly 100% reflection on copper foil. That is to say, the conventional CO2 gas laser is an ineffective drilling tool on copper foil.
Moreover, conformal mask is used in the HDI process. The copper foil surface is blackened so as to effectively absorb light by the black oxidized layer and the conventional gas laser drilling can be applied. Alternatively, copper foil is thinned first and then drilled by gas laser. The above-mentioned means still have the problems of low production rate, complex process and high cost.